Multi-station discrete media printing systems are known and widely used to imprint objects of various media, such as, but not limited to, garments (e.g. T-shirts), packaging material and various parts of industrial products; the latter include, but not limited to, casings, front panels, labels and nameplates. The terms “discrete medium” and “object” will be used in the sequel interchangeably. Most such systems are configured circularly, and thus are referred to as carousels, but other configurations, such as a linear configuration are possible. FIG. 1 shows, by way of example, a top-view sketch of a typical carousel system, this one—with eight stations (denoted by dashed rectangles). It includes a rotating member with eight tablets, equally spaced around a circle, and is designed to rotate in steps of 45 degrees and to rest between steps while each tablet is at a corresponding station; during a complete rotation, each tablet rests consecutively at each station. The tablets serve as carriers for objects to imprinted. Usually a first station is a loading station, in which an object to be imprinted is loaded onto the tablet then resting there, and the last station is an unloading station, in which an imprinted object is unloaded from the tablet then resting there. Some or all of the other stations are equipped to perform certain processing to the objects—each station applying a unique process to an object resting thereat. Such processes may include, for example, cleaning, painting (e.g. by an airbrush), drying, imprinting an image and applying a protective coat. Imprinting an image may be done in several ink colors, in which case each color is usually imprinted at a corresponding station. Image imprinting is most commonly done by a screen-printing (also known as silk-screen) process (using a flat- or rotary screen). An additional type of process, intermediate between painting and image imprinting, which may used at some station, applies an opaque paint to certain portions of the object's surface—usually to serve as background for a subsequently imprinted image. In the context of the present disclosure, the terms “printing” and “imprinting” are to be understood as including any process of selectively laying down a substance on a medium or an object, resulting in a specified image or a specified area pattern of the substance.
Image printing in present-day multi-station printing system, using conventional printing technologies (such as the aforementioned screen-printing process), typically involves a printing form (e.g. a screen, in the case of screen-printing), in which there is an image-wise distribution of inking- and non-inking areas. This distribution is fixed for any one print run and causes identical images to be printed on all objects passing the corresponding station. When a different image is to be imprinted, a new form must be prepared and installed. Such a change involves expenditure of time, effort and materials and thus is costly. For short print runs the costs of changing a printing form become relatively high and for very short runs may become prohibitive. For the extreme case that every object carry a different (or even partially different) image, the use of conventional printing, with changing printing forms, becomes totally impractical. Yet short runs and, moreover, single-print (i.e. custom image) runs are increasingly desired. It should be noted that often a different image also requires a differently shaped background paint.
Another shortcoming of screen-printing, used in current multi-station printing systems, is that it does not readily lend itself to printing images with process color (i.e. where a large number of color values is achievable by printing various proportions of three or four basic ink colors). This is due to the low resolution and inaccurate registration between impressions at successive stations that are inherent to this technology.
There is thus a need for, and it would be advantageous to have, a multi-station discrete-media printing system that includes at least one printing station capable of printing images that may be frequently changed—preferably even between successively positioned individual objects. There is a further need for, and it would be advantageous to have, such a system that permits printing with process colors.